The fossils were both found near the town of Kotelnich along the Vyatka River in European Russia.

The first, which the researchers have dubbed ‘Gorynychus masyutinae’, was a wolf-sized carnivore, while the second, named ‘Nochnitsa geminidens’, was a smaller, long-snouted carnivore with needle-like teeth.

Both new species are named after legendary monsters from Russian folklore, due to their ‘menacing’ appearances.

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The fossils were both found near the town of Kotelnich along the Vyatka River in European Russia (Image: Christian Kammerer)

The findings help to improve scientists’ understanding of the early evolution of mammals after the mid-Permian extinction, around 260 million years ago.

The researchers suggest that in the late Permian ecosystem, giant, tiger-sized sabre-toothed predators dominated over

But by the mid-Permian, smaller carnivores dominated.

Christian Kammerer, who led the study, said: “In between these extinctions, there was a complete flip-flop in what roles these carnivores were playing in their ecosystems - as if bears suddenly became weasel-sized and weasels became bear-sized in their place.

“Kotelnich is one of the most important localities worldwide for finding therapsid fossils - not only because they are amazingly complete and well-preserved there, but also because they provide an all-too-rare window into mammal ancestry in the Northern Hemisphere during the Permian."